MINUTES OF MEETINGS. 199 



at the time. Lake Erie has a fluctuation of seven feet 

 between the known extremes, and of five feet between the 

 mean of the highest and lowest months. Probably the 

 other lakes have as great a range of surface. It is neces- 

 sary, therefore, to have a bench mark on each of them, 

 representing its mean surface, corresponding to the mean 

 tide on the ocean, before the true elevation can be deter- 

 mined. 



_2^There must be also some inclination of surface towards 

 the outlet, causing a difi'erence of elevation between the 

 two ends of a lake, as, for instance, at Buffalo and at 

 Toledo. This difference is not known. The mean level at 

 a central point, like Cleveland, would, however, represent 

 closely the elevation of the lake. 



To determine the mean level accurately, daily observa- 

 tions are necessary, covering a space of at least twenty- 

 five years. The attention of the Government, and particu- 

 larly of the Chief of the Topographical Bureau, was long 

 since called to this subject. Soundings and harbor works, 

 docks, warehouses and channels, that are liable to changes 

 of five feet in the depth of the water, cannot be a safe reli- 

 ance for commercial purposes. 



Although some ofiicers of the Topographical Corps, in 

 charge of harbor constructions, had, on their own respon- 

 sibility, kept detached water registers, they were not 

 encouraged by the head of the Bureau, and it was not until 

 1859 that Capt. Meade, who is now in charge of the lake 

 surveys, procured an appropriation for that purpose. Be- 

 fore that year, the members of the Geological Surveys of 

 Ohio and Michigan, and the Regents of the New York 

 University, with the assistance of civil engineers, collected 

 what information we have concerning the fluctuations of 

 level. 



At least two daily registers are now kept under the 

 direction of Capt. Meade, on all the lakes. There will thus 



